A High-electron-mobility transistor (HEMT), also known as heterostructure FET (HFET) or modulation-doped FET (MODFET), is a field-effect transistor incorporating a junction between two materials with different band gaps forming a heterojunction as the channel instead of a doped region (as is generally the case for MOSFET). A commonly used material combination is GaAs with AlGaAs, though there is wide variation, dependent on the application of the device. Devices incorporating more Indium (In) generally provide better high-frequency performance, while in recent years, gallium nitride HEMTs have been employed due to their high-power performance. Like other FETs, HEMTs are used in integrated circuits as digital switching devices. These devices can also be used as amplifiers for large amounts of current using a small voltage as a control signal. Both of these uses are made possible by the device's unique current-voltage characteristics. For instance, HEMT transistors can operate at higher frequencies than ordinary transistors, up to millimeter wave frequencies, and are often used in high-frequency products such as cell phones, satellite television receivers, voltage converters, and radar equipment. They are also widely used in satellite receivers, in low power amplifiers, and in the defense industry.